MINERAL PROPERTY INTEREST - Mineral Property Interests (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Mineral Property Interests
Purchase price		$ 450
Mineral property interests	$ 242,107		$ 242,640
Amortization of mineral property interests and asset retirement obligations	533	322
El Gallo 1 mine
Mineral Property Interests
Amortization of mineral property interests and asset retirement obligations	$ 500	$ 300